The greater scale of integration and miniaturization of semiconductor devices in recent years has resulted in many diverse patterns being formed on the wafer and makes it ever more important to evaluate and measure the dimensions and shapes of these patterns. How fast these measurement points can be detected is critical for quickly and automatically testing the numerous measurement points. During fast detection of measurement points, it is necessary to focus on the pattern after shifting to the measurement point and to also set the desired magnification (scale) for observing that point.
In charged particle optical systems, the conditions for focusing on the wafer are determined by the acceleration voltage of the charged particle supply, the voltage applied to the wafer, and the height of the wafer.
In the method disclosed for example in JP-A No. 126573/1999, a laser beam is irradiated onto the wafer, the height of the wafer is detected by using that reflected light, and the height information obtained in this way is fed back to an objective lens control system serving as one control device for the charged particle optical system, and the necessary excitation voltage is applied to the objective lens at the same time that movement to the observation point ends.